Nitrate formulations



United States Patent NITRATE FORMULATIONS Clarence C. Harvey, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application July 29, 1954, Serial No. 446,683

7 Claims. (Cl. 260-467) This invention relates to aliphatic mononitrate ester formulations.

Aliphatic mononitrate esters, particularly those containing up to 4 carbon atoms are useful monopropellants. This utility takes advantage of the high specific energy content of such esters which is liberated on combustion and thus provides useful kinetic energy at low cost. In addition, aliphatic mononitrate esters are efiective as additives to diesel fuels. In this capacity, these esters act as cetane improvers by reducing the delay of ignition in the compression ignition engine. Again, an advantage in using such esters is that gain in cetane value is acquired at a minimum of cost.

Commercial grade aliphatic mononitrate esters have an inherent tendency of forming corrosion products when in contact with ferrous metal surfaces, particularly during storage and shipment. This is undesirable as these corrosion products tend to plug up filter screens and orifices such as in diesel injectors, result in metal deposits in combustion chambers and also produce product discoloration.-

Another problem which is somewhat related to corrosion tendency is increase in acid number; that is, on storage theabove esters tend 'to manifest an increase in acid content. This results in disruption of commercial specifications imposed on such nitrates and may result in severe corrosion, particularly of metallic surfaces of drums and the like.

Some of these problems may be overcome by the use of plastic liners in shipping containers such as epoxy resin coatings, or by the use of non-ferrous metal containers such asalurninurn. However, these alternatives are,not economically practicable inasmuch as the increase in cost oftentimes defeats the purposes for which the mononitrate esters are intended.

Among the objects of this invention is that of providing improved aliphatic mononitrate ester formulations not suffering the disadvantages discussed above. Another object of this invention is to provide methods of protecting mononitrate esters against contamination by corrosion products which normally occurs when such esters are in contact with ferrous metal surfaces. Other objects of my invention will be apparent from the ensuing description.

The above and other objects of this invention are accomplished by providing a composition of matter consisting essentially of a mononitrate ester of an aliphatic monohydric alcohol normally susceptible to contamination by corrosion products when in contact with a ferrous metal surface and, present in amount sufiicient to inhibit such contamination, an aliphatic polyhydric alcohol having in the molecule from 2 to 6 carbon atoms and from 2 to 4 hydroxyl groups, at least one of said groups being attached to a primary carbon atom. A preferred embodiment of this invention relates to the use as corrosion inhibitors for the above-described esters, an allphatic polyhydric alcohol as above-described containing a plurality of hydroxyl groups attached to difierent primary carbon atoms. Such alcohols have been found to be evenv more effective in accomplishing the objects of this invention.

The amount of alcohol stabilizer present in the formulations of this invention is from about 0.01 to about 10 per cent by weight of the nitrate ester, although amounts of the order of about 0.01 to about 1 per cent are generally preferrcd. In most instances, the .low solubility of the majority of the above-described polyhydric alcohols in the mononitrate esters of aliphatic monohydric alcohols results in the formation of a separate liquid or solid phase of the alcohol stabilizer along with a saturated solution of polyhydric alcohol in the esters. Such heterogeneous formulations are suitable according to this invention, although it is preferable to form saturated solutions of polyhydric alcohol in mononitrate ester so that there are provided completely homogeneous formulations of enhanced storage and shipping characteristics.

Aliphatic polyhydric alcohols useful according to this invention include ethylene glycol, propylene glycol, isobutylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol glycerol, 1,1,1-trimethylol propane, 1,1,1-trimethylol ethane, D-, L- and meso-erythritol, pentaerythritol, and the like. In other words, any aliphatic polyhydric alcohol having from 2 to 6 carbon atoms and from 2 to 4 hydroxyl groups, at least one of which groups ..is attached to a primary carbon atom is satisfactory so long as it is free from other functional groups.

The above alcohols are, for the most part, available as articles of commerce. Thus, the methods of preparing them are well known and can be found in almost any standard reference manual of organic chemistry.

Mononitrate esters of aliphatic monohydric alcohols stabilized according to this invention are those which contain from I to about 18 carbon atoms in the molecule and which consist essentially of the elements carbon, hydrogen, nitrogen, and oxygen. The principles of this invention are also applicable to certain sulfur-containing mononitrate esters, that is, mononitrate esters of aliphatic monohydric alcohols in which the aliphatic portion of the molecule contains one or more sulfur atoms. My invention is thus useful in stabilizing mononitrate esters of monohydric alkyl alcohols such as methyl nitrate, ethyl nitrate, n-propyl nitrate, isopropyl nitrate, and likewise the several butyl nitrates, amyl nitrates, octyl nitrates, decyl nitrates, dodecyl nitrates, and up to and including the octadecyl nitrates, or mixtures thereof. Similarly, such aliphatic mononitrate esters as p-ethoxy ethyl nitrate, p-n-propoxy ethyl nitrate, ,B-phenoxy ethyl nitrate, 'y-nhexoxy-n-propyl nitrate, ,B-(fl-ethoxyethyD-ethyl nitrate and like mononitrates containing up to about 18 carbon atoms in the'molecule in which the aliphatic chain contains one or more oxygen atoms can be protected by my inventions. Corresponding sulfur compounds such as thioethoxy ethyl nitrate and the like can be similarly stabilized.

The mononitrate esters of my improved formulations may be prepared by any of several known methods including direct nitration with nitric acid or nitration with a mixture of nitric and sulfuric acids. Such methods are known to one skilled in the art and may be found in standard organic chemistry reference books.

To prepare the formulations of this invention appropriate quantities of mononitrate ester and polyhydric alcohols as described above are brought together and by means of shaking, stirring, or other means of physical agitation, there is provided a one or two-phase system depending upon the amount of polyhydric alcohol employed. If desired, excess undissolved alcohol may be separated from the nitrate ester saturaed with the same means of decantation or like procedures.

Various formulations of this invention were prepared by mixing different quantities of polyhydric alcohols with I; typ cal aliphatic niononitrate esters. To demonstrate the enhanced storage characteristics of these formulations they were placed in a glass container in which a strip of ordinary mild steel was submerged, this being the usual material of construction encountered in normal commercial storage and shipping of the mononitrate esters. These containers were then stored while periodically observing visually any changes which may have occurred.

For comparative purposes, base line runs using amyl and n-propyl nitrates not containing stabilizers were likewise stored. The results of these tests are shown in the following table.

Table Amt. oi Stab., Percent Nitrate Stabilizer Remarks n-propyl nitraten-anryl nitrate. glycerol. 0. 05

Substantially no corrosion of the metal and no "contamination of product after four months.

Very slight corrosion observed but no contamina: tion of product atter four months.

No corrosion or product contamination otter months.

n-propyl nitrate-- do 1.

Do do 3.0

1,1,l-tri- 0.

m e t h ylol.

1,1,1-trim e t h ylol ethane.

p ontaerythrltol.

0.05 Slight corrosion but no product contamination alter three months.

Equally good results are obtained using other formula.- tions of this invention similar to those described above. For example, such formulations as one per cent of ethylene glycol with fi-ethoxy ethyl nitrate, 0.4 per cent of tetramethylene glycol with isopropyl nitrate, one per cent of isobutylene glycol with ethyl nitrate, 2 per cent of pentamethylene glycol with sec-butyl nitrate, per cent of propylene glycol with isooctyl nitrate, 4 per cent of mesoerythritol with mixed octadecyl mononitrates, 8 per cent of tetramethylene glycol with fl(;3-ethoxy-ethyl)-ethyl nitrate, etc., show substantially no contamination when subjected to the above test procedure.

Only alight.

Additional advantages of this invention include: (1) prolonged life of storage containers, (2) s no change in requisite physical and chemical properties of the mononitrate esters such as viscosity; vapor pressure; burning characteristics, such as ignition temperature and heat content per unit weight; freezing point or the like.

For identification purposes various dyestuifs may be employed in the improved formulations of this invention.

I claim:

1. A nitrate formulation consisting essentially of amononitrate ester of a monohydric alcohol selected from the group consisting of alkyl nitrates, alkoxy alkyl nitrates, and phenoxy alkyl nitrates containing from 1 to about 18 carbon atoms which is normally susceptible to contamination by corrosion products when in contact with a ferrous metal surface and, from about 0.01 to 10 per cent by weight of an aliphatic polyhydric alcohol having in the molecule from 2 to 6 carbon atoms and from 2 to 4 hydroxyl groups, at least one of said groups being attached to a primary carbon atom.

2. The composition of claim 1 in which said aliphatic polyhydric alcohol is further characterized in that it contains a plurality of hydroxyl groups attached to difierent primary carbon atoms.

3. The composition of claim 1 in which said mononitrate ester is a mononitrate ester of an alkyl monohydricalcohol containing from 1 to about 18 carbon atoms in the molecule.

4. Process of stabilizing a mononitrate ester of a monohydric alcohol selected from the group consisting of alltyl nitrates, alkoxy alkyl nitrates, and phenoxy alkyl nitrates containing from 1 to about 18 carbon atoms normally susceptible to'contaminafion by corrosion products when in contact with a ferrous metal surface which comprisesblending with said ester from about 0.01 to 10 per cent by weight of an aliphatic polyhydric alcohol having in the molecule from 2 to 6 carbon atoms and from 2 to 4 hy droityl groups, at least one of said groups being attached toaprimary carbon atom.

5; Process of claim 4 in which said aliphatic polyhydric alcohol is further characterized in that it contains a plurality of hydroxyl groups attached to difierent primary carbon atoms.

6. A nitrate formulation consisting essentially of amyl nitrate and from about 0.01 to glycerol.

7. The composition of claim 6 wherein the amount of glycerol is 0.05 per cent by weight.

References. Cited inthe file of this patent UNITED STATES PATENTS Schiermeier et al Sept. 20, 1949 10 per cent by weight of 

4. PROCESS OF STABILIZING A MONONITRATE ESTER OF A MONOHYDRIC ALCOHOL SELECTED FROM THE GROUP CONSISTING OF ALKYL NITRATES, ALKOXY ALKYL NITRATES, AND PHENOXY ALKYL NITRATES CONTAINING FROM 1 TO ABOUT 18 CARBON ATOMS NORMALLY SUSCEPTIBLE TO CONTAMINATION BY CORROSION PRODUCTS WHEN IN CONTACT WITH A FERROUS METAL SURFACE WHICH COMPRISES BLENDING WITH SAID ESTER FROM ABOUT 0.01 TO 10 PER CENT BY WEIGHT OF AN ALIPHATIC POLYHYDRIC ALCOHOL HAVING IN THE MOLECULE FROM 2 TO 6 CARBON ATOMS AND FROM 2 TO 4 HYDROXYL GROUPS, AT LEAST ONE OF SAID GROUPS BEING ATTACHED TO A PRIMARY CARBON ATOM. 